1. Field of the Invention
This invention relates to light-emitting compounds and compositions, as well as light-emitting devices that include the light-emitting compounds or compositions.
2. Description of the Related Art
Organic light-emitting devices have been widely developed for flat panel displays, and are moving fast toward solid state lighting (SSL) applications. Organic Light Emitting Diodes (OLEDs) comprise a cathode, a hole transporting layer, an emissive layer, an electron transporting layer, and an anode. Light emitted from an OLED device is the result of recombination of positive charges (holes) and negative charges (electrons) inside an organic (emissive) layer. The holes and electrons combine within a single molecule or a small cluster of molecules to generate excitons, which are molecules in an excited state, or groups of organic molecules bound together in an excited state. When the organic molecules release the required energy and return to their stable state, photons are generated. Organic materials which emit the photons are referred as an electro-fluorescent material or electro-phosphorescent material depending on the nature of the radiative process. Thus the OLED emissive compounds may be selected for their ability to absorb primary radiation and emit radiation of a desired wavelength. For blue emitters, for example, emission within principle emission bands of 440 to 490 nm may be desirable.
SSL applications may require a white OLED device to achieve greater than 1,500 lm brightness, a color rendering index (CRI) greater than 70, and an operating time greater than 100,000 hours at 100 lm/w. There are many approaches for generating white light from an OLED, but two common approaches are: direct combination of red, blue, and green light using either lateral patterning or vertical stacking of three emitters; and partial down conversion of blue light in combination with yellow phosphors. Both of these common approaches may be more effective if a highly efficient chemical- and photo-stable blue dye is employed. However, blue emitters may be less stable than dyes which emit other colors. Furthermore, there are very few blue emitting devices showing a CIE y value below 0.2 yet still with respectable efficiency. Thus, the development of deep blue emitters with good stability and high luminescence efficiency is desirable to effectively reduce power consumption and generate emission of different colors.